The principal area of focus for this project is the identification of heritable characteristics of ion transport which may distinguish individuals with a primary affective disorder from normal controls. A study of sodium potassium stimulated adenosine triphosphatase (Na+ -K+ - ATPase), to cation transport enzyme, is in progress. An assay has been developed to determine the level of this membrane enzyme in bipolar and unipolar depressed patients and in normal controls. A twin study will serve to determine heritability of this enzyme.